Antimicrobial steel and related methods

ABSTRACT

A method of reducing viability of a microbe is provided. An illustrative method comprises contacting a microbe with an antimicrobial surface comprising a copper-alloy steel comprising an iron matrix and copper nanoprecipitates distributed throughout the iron matrix, wherein the copper-alloy steel comprises: Cu in a range from 0.5 weight % to 5.0 weight %; C in a range from 0.03 weight % to 0.10 weight %; Mn in a range from 0.20 weight % to 5.0 weight %; Ni in a range from 0.0 weight % to 6.0 weight %; Al in a range from 0.0 weight % to 4.0 weight %; Nb in a range from 0.0 weight % to 0.10 weight %; Si in a range from 0.0 weight % to 2.0 weight %; Mo in a range from 0.0 weight % to 2.0 weight %; Ti in a range from 0.0 weight % to 2.0 weight %; V in a range from 0.0 weight % to 2.0 weight %; Cr in a range from 0.0 weight % to 8.0 weight %; and a balance of Fe. The antimicrobial surfaces are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. provisional patent application No. 63/011,646 that was filed Apr. 17, 2020, the entire contents of which are incorporated herein by reference.

BACKGROUND

Stainless steels are used in hospitals, health care facilities, public transportation, appliances, food manufacturing and service, etc. because of their corrosion resistance and clean appearance. However, stainless steels have little or no antimicrobial properties, rendering them ineffective against the transmission of pathogens. SARS-CoV-2 coronavirus is known to survive several days on stainless steel surfaces. Thus, touching contaminated surfaces is likely to spread COVID-19 infection.

SUMMARY

Provided are antimicrobial surfaces and related methods.

An illustrative method of reducing viability of a microbe comprises contacting a microbe with an antimicrobial surface comprising a copper-alloy steel comprising an iron matrix and copper nanoprecipitates distributed throughout the iron matrix, wherein the copper-alloy steel comprises: Cu in a range from 0.5 weight % to 5.0 weight %; C in a range from 0.03 weight % to 0.10 weight %; Mn in a range from 0.20 weight % to 5.0 weight %; Ni in a range from 0.0 weight % to 6.0 weight %; Al in a range from 0.0 weight % to 4.0 weight %; Nb in a range from 0.0 weight % to 0.10 weight %; Si in a range from 0.0 weight % to 2.0 weight %; Mo in a range from 0.0 weight % to 2.0 weight %; Ti in a range from 0.0 weight % to 2.0 weight %; V in a range from 0.0 weight % to 2.0 weight %; Cr in a range from 0.0 weight % to 8.0 weight %; and a balance of Fe. The antimicrobial surfaces are also provided.

Other principal features and advantages of the disclosure will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the disclosure will hereafter be described with reference to the accompanying drawings.

FIG. 1 shows an atom probe image of a copper alloy steel comprising a ferritic matrix and copper nanoprecipitates distributed throughout the ferritic matrix. The copper alloy steel comprises from 1.5 weight % to 4.5 weight % copper.

FIG. 2 shows the evolution of the number of H₂O₂, hydroxyl radicals, oxygen, and water molecules as a function of time at room temperature from a surface of a bcc Cu nanoprecipitate in an illustrative antimicrobial surface.

FIG. 3 illustrates flat and textured controlled antimicrobial surfaces.

FIG. 4 illustrates the bactericidal properties of illustrative antimicrobial surfaces.

DETAILED DESCRIPTION

The present antimicrobial surfaces comprise a copper alloy steel comprising an iron matrix and copper nanoprecipitates distributed throughout the iron matrix. The crystal structure of the iron of the iron matrix may be ferritic, martensitic, or partially martensitic. The copper of the copper alloy steel is generally present in the iron matrix at an amount in a range of from 0.5 weight % to 5.0 weight % as compared to the total weight of the copper alloy steel. This includes from 0.5 weight % to 4.0 weight %, from 1.0 weight % to 4.0 weight %, from 0.5 weight % to 3.0 weight %, and from 1.0 weight % to 3.0 weight %. The copper alloy steel generally comprises other elements in addition to the copper and the carbon and iron of the matrix. These other elements may include Mn, Ni, Al, Nb, Si, Mo, Ti, V, and combinations thereof. Illustrative amounts (in weight %) of these elements are as follows: C may range from 0.03 to 0.10; Mn may range from 0.20 to 5.0; Ni may range from 0.0 to 6.0; Al may range from 0.0 to 4.0; Nb may range from 0.0 to 0.10; Si, Mo, Ti, and V may each range (independently) from 0.0 to 2.0. In all cases, the balance is iron. Chromium is another element which may be added to the copper alloy steel, including in amounts (in weight %) of from 0.0 to 8.0. The addition of chromium (Cr) is further described below.

Thus, in embodiments, the copper alloy steel comprises or consists of Fe, Cu, C, Mn, and one or more of Ni, Al, Nb, Si, Mo, Ti, V, and Cr. In embodiments, the copper alloy steel comprises or consists of Fe, Cu, C, Mn, Ni, and optionally, Cr. In embodiments, the copper alloy steel comprises or consists of Fe, Cu, C, Mn, Ni, Al and, optionally, Cr. In embodiments, the copper alloy comprises or steel consists of Fe, Cu, C, Mn, Ni, Nb, Si, and optionally, Cr. In embodiments, the copper alloy steel comprises or consists of Fe, Cu, C, Mn, Ni, Al, Nb, Si, and optionally, Cr. In embodiments, the copper alloy steel comprises or consists of Fe, Cu, C, Mn, Ni, Nb, Si, Ti, and optionally, Cr. In each of these embodiments, the amounts of each element may be within the ranges described above.

In embodiments, certain elements are not present in the copper alloy steel (or in the antimicrobial surface), i.e., in these embodiments, the copper alloy steel does not comprise these elements. These include one, more than one, or all, of S, P, Co, Sn, and N.

In embodiments, the copper alloy steel has one of the compositions shown in Table 1, below. However, in each of these embodiments, chromium may be present in the amounts described above. In such embodiments, the copper alloy steel may be considered to consist of the elements shown below at the amounts shown below.

TABLE 1 Illustrative Compositions for Copper Alloy Steels. Amounts are weight %. Cu C Mn Ni Al Nb Si Ti Fe 1.29 0.05 0.50 2.70 0.6 0.0 0.0 0.0 Balance 2.48 0.06 0.52 2.58 0.59 0.06 0.51 0.0 Balance 2.50 0.06 1.47 2.59 0.54 0.06 0.52 0.0 Balance 2.50 0.05 1.50 4.00 1.00 0.0 0.0 0.0 Balance 3.00 0.05 3.00 4.00 1.50 0.07 0.53 0.0 Balance 4.00 0.05 4.00 4.00 1.00 0.07 0.48 0.0 Balance 1.49 0.03 0.49 0.84 0.0 0.06 0.40 0.03 Balance 1.30 0.06 0.50 0.90 0.0 0.06 0.39 0.10 Balance 0.94 0.07 0.87 0.49 0.0 0.07 0.30 0.03 Balance

The antimicrobial surface may consist of any of the copper alloy steels described herein.

An atom probe tomography image of a copper alloy steel comprising 2.5 weight % copper is shown in FIG. 1. The copper alloy steel was formed as described in Kapoor, M. et al., Acta Materialia 73 (2014) 56-74 (hereby incorporated by reference in its entirety), with solution treatment at 950° C., followed by water-quenching and aging at 500° C. for 2 hours. As shown in FIG. 1, the copper is in the form of the nanoprecipitates, although some copper may be present outside of the nanoprecipitates, including in solid solution. These nanoprecipitates are generally spherical in shape, but the term “spherical” encompasses irregularly shaped nanoprecipitates as well as nanoprecipitates having a more elongated morphology. All of the nanoprecipitates in the copper alloy steel of FIG. 1 may be considered spherical. The copper nanoprecipitates may be characterized by an average radius. (By “average” it is meant an average value over a representative number of nanoprecipitates. The average value may be obtained from atom probe images such as that shown in FIG. 1.) The average radius for the copper alloy steel of FIG. 1 is 2.0±0.6 nm. However, in general, the average radius may vary depending upon the amount of copper in the copper alloy steel and heat treatment. In embodiments, the copper alloy steel has an average radius in a range of from 0.5 nm to 20 nm. This includes an average radius in a range of from 0.5 nm to 10 nm, and from 0.5 nm to 5 nm.

The average center-to-center spacing λ between neighboring Cu nanoprecipitates also depends upon the amount of copper in the copper alloy steel and heat treatment. The value of λ is given by

${\frac{d}{2}\sqrt{\frac{3\pi}{4f}}},$

wherein d is the average nanoprecipitate diameter and f is the volume fraction. However, in embodiments, λ is in a range of from 5 nm to 200 nm, from 10 nm to 150 nm, and from 25 nm to 100 nm. Comparing the average nanoprecipitate radius and the average λ to the size of a microbe such as SARS-CoV-2 (having a diameter of about 120 nm), it is clear that a microbe on a surface of the copper alloy steel will be in contact with many copper atoms simultaneously.

The copper nanoprecipitates in the copper alloy steel may be further characterized by their crystal structure. In embodiments, the crystal structure is bcc, i.e., the copper nanoprecipitates are bcc copper nanoprecipitates. Theoretical calculations were conducted to examine the interaction of microbes coming into direct contact with copper atoms at the surfaces of bcc copper nanoprecipitates. As an example, molecular dynamics simulation using the large-scale atomic/molecular massively parallel simulator (LAMMPS) was conducted on the interaction between a bcc Cu (111) stepped surface and 150 hydrogen peroxide (H₂O₂) molecules at room temperature (H₂O₂ is produced by human cells and many bacteria species). FIG. 2 displays the evolution of the number of H₂O₂, hydroxyl radicals, molecular oxygen, and water molecules as a function of time. The fragmentation of H₂O₂ upon contact with Cu is almost immediate, producing hydroxyl radicals, oxygen, and water. These changes are accompanied by the oxidation of Cu to form Cu⁺, strongly suggestive of Fenton-like chemical reactions. The process appears to reach steady state after about 60 ps and is indicative of the occurrence of a back-reaction, i.e., formation of H₂O₂ from initial reaction products. Both H₂O₂ and hydroxyl radicals are reactive oxygen species that play an important role in antimicrobial action.

As noted above, the methods of Kapoor, M. et al. may be used to form the copper alloy steels. Other methods which may be used are those described in Fine, M. E., et al., Metallurgical and Materials Transactions A, Vol. 41A, December 2010, (hereby incorporated by reference in its entirety). Some embodiments of such copper alloy steels have been used as weather steels for civil infrastructure applications, such as bridges, due to their low-temperature toughness, weldability, and weather resistance. However, these copper alloy steels have not previously been considered for use in the very different application of antimicrobial steels.

As noted above, the copper alloy steel may further comprise an amount of chromium (Cr). The amount may be selected to provide enough Cr so that a chromium oxide layer forms on a surface of the copper alloy steel (thereby inhibiting rust formation) but not so much Cr that the incorporation of copper and copper nanoprecipitates into the chromium oxide layer is prevented. As noted above, the amount may be in a range of from 0.0 weight % to 8.0 weight %.

In embodiments, a surface of the copper alloy steel is textured. Different types of texture may be used and a variety of known techniques may be used to achieve such texture types such as buffing, etching, laser machining, forging, forming, milling, polishing, rolling, turning, etc. The texture type (e.g., morphology and dimensions) may be selected to increase (e.g., maximize) the amount of surface area of the microbe in contact with the antimicrobial surface. Thus, the texture type may depend upon the target microbe. Illustrative texture types include grooves (one dimensional (1D) texture type), pillars (2D), dimples (2D texture type), and the like in any density and distribution. Such texture types effectively provide the surface having a plurality of ridges (1D)/peaks (2D) separated by a plurality of channels (1D)/valleys (2D). A cross-section of these texture types is shown in the right image of FIG. 3. The width of the channel/valley and the height of the peak-to-valley (ridge-to-channel) (both of which may be an average value) be selected to increase (e.g., maximize) the amount of surface area of the microbe in contact with the antimicrobial surface. This may be achieved by using texture type dimensions (e.g., the width/height described above) that match the diameter of the target microbe. As shown in FIG. 3, for SARS-CoV-2 coronavirus, dimensions of about 100 nm are particularly useful to maximize contact. In other embodiments, the surface of the copper alloy steel is untextured, i.e., flat.

The present antimicrobial surfaces are characterized by antimicrobial properties which are exhibited upon contact with a microbe. Without wishing to be bound to a particular theory, these antimicrobial properties may include an ability to induce dissociation of certain components, e.g., proteins, of the microbes, thereby reducing, including destroying, the viability of the microbes. By way of example, molecular simulations were conducted examining the interactions of a molecular model of the S-protein of SARS-CoV-2 coronavirus with an illustrative antimicrobial surface and for a control surface free of copper. The control surface free of copper may have the same composition as the antimicrobial surface except is free of copper. Such a control surface may be referred to as a comparative surface. The simulations showed that the S-protein quickly dissociates in the presence of copper.

The present antimicrobial surfaces may be used against microbes of any variety. The microbes include any bacteria, e.g., an Escherichia coli (E. coli) bacterium. The microbes include any virus, e.g., SARS-CoV-2 coronavirus, or ϕ-6. Contact between the antimicrobial surfaces and the microbes may result from, e.g., touching, splattering, spilling, spraying, etc., the antimicrobial surface with any material (e.g., a fluid, a sample, another surface, etc.) containing the microbes. Use of the antimicrobial surfaces effectively provides a method of reducing microbe viability, reducing infection due to a microbe, reducing transmission of such an infection, and the like.

The antimicrobial properties and efficacy of the present antimicrobial surfaces against microbes may be quantified in a variety of ways. However, such properties/efficacy can refer to a number of colony forming units (CFUs) (or percentage thereof) measured in a sample containing a target microbe after the sample and antimicrobial surface have been in contact for a particular period of time. This is illustrated in FIG. 4 showing the CFUs obtained from a sample of E. coli HCB84 after contact with two different illustrative antimicrobial surfaces, one comprising 2.5 wt % copper and one comprising 4.0 weight % copper, for 30 minutes. The results for control surfaces are also shown, including a copper-free “control” and pure copper “Cu”. Clearly, the CFUs for the illustrative antimicrobial surfaces are less than that of the copper-free control surface. Remarkably, the CFUs for the illustrative antimicrobial surfaces are less than 10 CFUs, a factor 30 less than that of the copper-free control surface. Moreover, the CFUs for the illustrative antimicrobial surfaces are nearly the same as that of pure copper. Another way to reference the antimicrobial properties/efficacy of the antimicrobial surfaces is to measure a half-life of a target microbe or a % kill of a target microbe. For example, the antimicrobial surface may be characterized by a half-life of a target microbe (e.g., SARS-CoV-2) on the antimicrobial surface that is shorter than the half-life of the target microbe on steel having a composition that is the same as the copper alloy steel except is free of copper. The half-life may be shorter by a factor of at least 5.

Due to their antimicrobial properties, the present antimicrobial surfaces are used in environments in which microbes are present, or are suspected of being present, including in quantities that are more likely than not to result in infection of a mammalian (e.g., human) subject. These environments include those frequented by the public, such as hospitals and health care facilities, schools, public transportation centers and vehicles, public restroom facilities, recreation centers, shopping centers, food service facilities, walkways of a bridge, etc. In embodiments, the environment is an indoor environment, e.g., enclosed within one or more walls such as a building, vehicle, tent, pavilion, etc. They may also be used to make pet containers and chains.

In general, the present antimicrobial surfaces may be incorporated into any article (which encompasses devices, appliances, etc., and components thereof) in which steel (or other materials, such as similar alloys and metals, glass, ceramics, plastics, wood) is typically used and for which antimicrobial properties are desired. In other words, the antimicrobial surfaces may be used to replace steel (or a similar material as mentioned above) in such articles in order to render the steel/materials antimicrobial. However, the type of article is often one which is configured for use by or contact with humans, including human body parts such as hands, as well as fluids or samples from humans. Such use generally refers to regular use, as opposed to incidental use. Non-limiting examples of such articles include handles, hand-holds, hand rails, doors, countertops, bed hardware, hardware in restroom facilitates, etc. These are all surfaces which are touchable by human body parts, e.g., hands, and which come into frequent contact with members of the public. The articles do not include those used in civil infrastructure applications, such as rebars in concrete. In embodiments, the articles do not include bridges.

The present disclosure encompasses the antimicrobial surfaces; articles, devices, appliances, and the like incorporating such antimicrobial surfaces; and methods of making and using the same.

The word “illustrative” is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “illustrative” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Further, for the purposes of this disclosure and unless otherwise specified, “a” or “an” means “one or more.”

All numeric values of parameters in the present disclosure are proceeded by the term “about” which means approximately. This encompasses those variations inherent to the measurement of the relevant parameter as understood by those of ordinary skill in the art. This also encompasses the exact value of the disclosed numeric value and values that round to the disclosed numeric value.

The foregoing description of illustrative embodiments of the disclosure has been presented for purposes of illustration and of description. It is not intended to be exhaustive or to limit the disclosure to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the disclosure. The embodiments were chosen and described in order to explain the principles of the disclosure and as practical applications of the disclosure to enable one skilled in the art to utilize the disclosure in various embodiments and with various modifications as suited to the particular use contemplated. It is intended that the scope of the disclosure be defined by the claims appended hereto and their equivalents. 

What is claimed is:
 1. A method of reducing viability of a microbe, the method comprising contacting a microbe with an antimicrobial surface comprising a copper-alloy steel comprising an iron matrix and copper nanoprecipitates distributed throughout the iron matrix, wherein the copper-alloy steel comprises: Cu in a range from 0.5 weight % to 5.0 weight %; C in a range from 0.03 weight % to 0.10 weight %; Mn in a range from 0.20 weight % to 5.0 weight %; Ni in a range from 0.0 weight % to 6.0 weight %; Al in a range from 0.0 weight % to 4.0 weight %; Nb in a range from 0.0 weight % to 0.10 weight %; Si in a range from 0.0 weight % to 2.0 weight %; Mo in a range from 0.0 weight % to 2.0 weight %; Ti in a range from 0.0 weight % to 2.0 weight %; V in a range from 0.0 weight % to 2.0 weight %; Cr in a range from 0.0 weight % to 8.0 weight %; and a balance of Fe.
 2. The method of claim 1, wherein the copper iron alloy does not comprise S, P, Co, Sn, and N.
 3. The method of claim 1, wherein the copper iron alloy comprises Fe, Cu, C, Mn, and one or more of Ni, Al, Nb, Si, Mo, Ti, V, and Cr.
 4. The method of claim 1, wherein the copper iron alloy comprises Fe, Cu, C, Mn, Ni, and optionally, Cr.
 5. The method of claim 1, wherein the copper iron alloy comprises Fe, Cu, C, Mn, Ni, Al and, optionally, Cr.
 6. The method of claim 1, wherein the copper iron alloy comprises Fe, Cu, C, Mn, Ni, Nb, Si, and optionally, Cr.
 7. The method of claim 1, wherein the copper alloy steel comprises Fe, Cu, C, Mn, Ni, Al, Nb, Si, and optionally, Cr.
 8. The method of claim 1, wherein the copper alloy steel comprises Fe, Cu, C, Mn, Ni, Nb, Si, Ti, and optionally, Cr.
 9. The method of claim 1, wherein the copper alloy steel is characterized by an average center-to-center spacing λ between neighboring copper nanoprecipitates in a range of from 5 nm to 200 nm.
 10. The method of claim 1, wherein the copper nanoprecipitates are bcc copper nanoprecipitates.
 11. The method of claim 1, wherein the iron matrix is ferritic, martensitic, or partially martensitic.
 12. The method of claim 1, wherein the antimicrobial surface is textured.
 13. The method of claim 1, wherein the contacting is carried out in an environment in which microbes are present, or are suspected of being present, in quantities that are more likely than not to result in an infection of a mammalian subject due to the microbes.
 14. The method of claim 1, wherein the contacting is carried out in an indoor environment.
 15. The method of claim 1, wherein the antimicrobial surface is part of an article configured for regular contact with a human body part.
 16. The method of claim 15, wherein the human body part is a hand.
 17. The method of claim 1, wherein the microbe is a virus.
 18. The method of claim 17, wherein the virus is SARS-CoV-2.
 19. An antimicrobial surface comprising a copper-alloy steel comprising an iron matrix and copper nanoprecipitates distributed throughout the iron matrix, wherein the copper-alloy steel comprises: Cu in a range from 0.5 weight % to 5.0 weight %; C in a range from 0.03 weight % to 0.10 weight %; Mn in a range from 0.20 weight % to 5.0 weight %; Ni in a range from 0.0 weight % to 6.0 weight %; Al in a range from 0.0 weight % to 4.0 weight %; Nb in a range from 0.0 weight % to 0.10 weight %; Si in a range from 0.0 weight % to 2.0 weight %; Mo in a range from 0.0 weight % to 2.0 weight %; Ti in a range from 0.0 weight % to 2.0 weight %; V in a range from 0.0 weight % to 2.0 weight %; Cr in a range from 0.0 weight % to 8.0 weight %; and a balance of Fe.
 20. The antimicrobial surface of claim 19, wherein the antimicrobial surface is part of an article configured for regular contact with a human body part. 